This invention relates to refrigerants, and more particularly, to a hydrocarbon refrigerant for use in a closed cycle refrigeration system.
Closed cycle refrigeration systems are well known and are typically used for household refrigeration, commercial refrigeration, freezer units, air conditioning units, heat pumps, and the like. Such systems use a refrigerant which can absorb surrounding heat while passing through an evaporator causing evaporation of the liquid refrigerant to a vapor. After the refrigerant has absorbed heat it is compressed thereby increasing its pressure. The high pressure fluid is passed through a condensing unit, typically located outside the refrigerated space. The heat in the refrigerant is given up to the surrounding, typically to the ambient air or to a liquid coolant. In the condenser, the refrigerant returns to its liquid state. It is then expanded through a throttle, valve or capillary tube to a low pressure fluid and is again sent into the refrigerating mechanism for absorbing heat.
In typical domestic refrigerators, the refrigerant temperatures in the evaporator are approximately 260.degree. K. and the condensing temperature is approximately 300.degree. K., which is slightly above ambient temperature. For freezing operations, the temperature may go a bit lower, and for air conditioning units, the temperature will be a bit higher. It should be understood, that reference to refrigeration in this application generally refers to such systems operating within the above general range of temperatures, including refrigeration, air conditioning and heat pumps, all of which are quite distinct from operating systems at cryogenic temperatures.
From a technical viewpoint, the refrigerant should have appropriate technical characteristics. For example, pressures under which it operates should be within a range of 1-20 atmospheres, and specifically, within the operation range of commercial refrigeration compressors. The high pressure boiling point should be approximately at ambient temperature. The low pressure dew point should be approximately at the freezing point of water.
Additionally, in order to be effective, the refrigerant should be non-toxic, non-flammable, and relatively inexpensive.
A wide group of refrigerants have typically been utilized for such refrigeration systems. Many of these are made up of compounds containing one or more of the halogens, including fluorine, chlorine, iodine and bromine. Those containing both chlorine and fluorine are generally referred to as halogenated chlorofluorocarbons. One group of such CFC refrigerants are sold under the brand name "Freon" which is a product of the DuPont Company. Various Freon formulations have been utilized, with each of these having differing temperature and pressure characteristics to conform to particular types of refrigeration systems. By way of example, Freon 12 (dichlorodifluoromethane) is a popular refrigerant in many refrigerator units. However, there are questions as to the environmental safety of such CFC's.
In addition to the halide refrigerants, other refrigerants have been suggested, such as ammonia methylchloride, and sulphur-dioxide. However, these are rather flammable or toxic and seldom utilized.
Certain types of refrigerants are utilized in open cycle refrigeration systems whereby the refrigerants are released to atmosphere. These are referred to as "expendable refrigerants" and include nitrogen, helium, and carbon dioxide. Certain hydrocarbons such as butane, ethane, and propane, are combustible and are not commonly used at all because of their combustible nature. In connection with cryogenic systems, however, it has been suggested to use hydrocarbons with nitrogen or helium. However, there has not been suggested the possibility of utilizing a mixture of hydrocarbons for effective closed cycle refrigeration use.